I. Field
The present disclosure relates generally to communication, and more specifically to techniques for performing frequency synchronization in a communication system.
II. Background
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technique that can provide good performance for some wireless environments. OFDM partitions the overall system bandwidth into multiple (K) orthogonal frequency subbands, which are also called carriers, subcarriers, tones, and so on. With OFDM, each subband is associated with a respective carrier that may be modulated with data. In the following description, “subband” and “carrier” are synonymous terms and are used interchangeably.
In an OFDM system, a transmitter processes (e.g., encodes, interleaves, and modulates) traffic data to generate modulation symbols and further maps the modulation symbols to the K total subbands. The transmitter then transforms the modulation symbols for each OFDM symbol period to the time domain and forms an OFDM symbol. The transmitter transmits the OFDM symbols to a receiver.
The receiver performs the complementary processing on the OFDM symbols received from the transmitter. The receiver transforms each received OFDM symbol to the frequency domain to obtain K received symbols for the K subbands. The received symbols are noisy and distorted versions of the modulation symbols sent by the transmitter. The receiver typically performs frequency synchronization to determine frequency error at the receiver. The frequency error may be due to difference in the oscillator frequencies at the transmitter and the receiver, Doppler shift, and so on. Frequency synchronization is challenging in certain channel environments such as low signal-to-noise ratio (SNR) conditions, fast fading, and so on. Furthermore, it is desirable to perform frequency synchronization quickly so that the processing overhead is as low as possible.
There is therefore a need in the art for techniques to perform frequency synchronization in a communication system.